This speeds up draw call validation.

BUG=angleproject:959

Change-Id: I8272e36201521f158823739a6604444fb5e66b6e
Reviewed-on: https://chromium-review.googlesource.com/266025Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>